1. Field of the Invention
The present invention relates to a printed circuit board and method for manufacturing the same, in which a ground construction of the printed circuit board can be selected based on wiring patterns and electric parts installed on the printed circuit board.
2. Description of the Background Art
As a typical flat display panel, a liquid crystal display device of an active matrix type is widely used. The liquid crystal display device includes a circuit board connected to the liquid crystal display panel via a connector such as a flexible substrate.
The circuit board is, for example, a printed circuit board (PCB) in which a plurality of conductive ground layers (traces) are laminated with interposing insulation layers. The printed circuit board is provided with a ground portion at its corner where the ground layers contained in respective multi layers are connected to an outer ground. The ground layers are often connected to the outer ground by a screw to fix the printed circuit board with an outer case of the display. However, the ground layers are sometimes separated from signal lines such as gate layers to avoid unfavorable electro-static action (i.e., are in a floating condition).
A printed circuit board having multi-conductive layers has been proposed in Japanese patent application 2004-104037, in which a ground connection using a shortest route from any location on the printed circuit board is described.
As described-above, in the case the printed circuit board is connected to the outer ground by a screw, noises from the outer ground may spread to the plurality of conductive ground layers in the printed circuit board through the screw. It is desirable for the noises from the outer ground to the printed circuit board to spread, for example, to the plurality of conductive ground layers in the printed circuit board through an appropriate route corresponding to a wiring pattern layout and types of electric elements installed on the printed circuit board.
However, the appropriate designing of the ground construction, which fits to a combination of the wiring pattern in the printed circuit board and the outer ground is accompanied with some difficulties in a first designing step. That is, it is difficult to determine whether the plurality of conductive ground layers should be set at a floating condition or be connected to the outer ground through the screw. Accordingly, the influence to a circuit operation of the printed circuit board by noises such as an electro-static noise, that spreads from the ground construction, becomes significant after installing the printed circuit board into the liquid crystal display device.